• Journal of the Korean Society for Heat Treatment
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• v.26 no.3
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• pp.113-119
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• 2013

Grain growth behaviors of hot-rolled AZ31 (Mg-3%Al-1%Zn) and AZ31-0.3%CaO alloys at elevated temperatures have been investigated in order to clarify the effect of CaO addition on grain stability of Mg-Al-based wrought alloy. The grain size of CaO-free alloy increased steeply from 673 K with an increase in annealing temperature from 573 to 773 K, whereas the grains of CaO-containing alloy were relatively stable up to 723 K. The activation energies for grain growth ($E_g$) were 12.2 and 18.3 kJ/mole between 573 and 673 K and 119.2 and 126.9 kJ/mole between 673 and 773 K in the AZ31 and AZ31-0.3%CaO alloys, respectively. This result indicates that grains in the CaO-added alloy possess higher thermal stability than CaO-free alloy. SEM observations on the annealed alloy samples revealed that higher grain stability resulting from CaO addition would be associated with the suppression of grain growth by Ca-related precipitate particles distributed in the microstructure.

• Journal of Biomedical Engineering Research
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• v.9 no.2
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• pp.215-224
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• 1988

Block copoly(L-lactide-${\gamma}$-benzyl-L-glutamate)was synthesized from L-lactide by cationic ring opening polymerization and ${\gamma}$-benzyl-L-glutamate N-carboxy anhydride by introducing amino group terminated poly(L-lactide). L-lactide was polymerized in the presence of stannous octate at $110^{\circ}C$ and ${\gamma}$-benzyl- L-glutamate was polymerized in the presence of NaH at room temperature. The synthesized monomers and copolymers were identified by IR and NMR. The Itermal properties of the copolymers were characterized by differential scanning calorimetry and thermogravimetry. The thermal stability and melting temperature(Tm) of the block copolymers were measured and discussed. The activation energies of thermal decomposition for the block copoly(L-lactide-${\gamma}$ benzyl-L-glutamate) were evaluated from the thermogravimetric data by Freeman and Carroll method.

• Journal of Astronomy and Space Sciences
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• v.31 no.4
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• pp.295-301
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• 2014

Whistler mode chorus wave is considered to play a critical role in accelerating and precipitating the electrons in the outer radiation belt. In this paper we test a conventional scenario of triggering chorus using THEMIS satellite observations of waves and particles. Specifically, we test if the chorus onset is consistent with development of anisotropy in the electron phase space density (PSD). After analyzing electron PSD for 73 chorus events, we find that, for ~80 % of them, their onsets are indeed associated with development of the positive anisotropy in PSD where the pitch angle distribution of electron velocity peaks at 90 degrees. This PSD anisotropy is prominent mainly at the electron energy range of ${\leq}$ ~20 keV. Interestingly, we further find that there is sometimes a time delay among energies in the increases of the anisotropy: A development of the positive anisotropy occurs earlier by several minutes for lower energy than for an adjacent higher energy.

• Journal of the Korean Applied Science and Technology
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• v.5 no.1
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• pp.41-51
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• 1988

Aliphatic aldehyde polyoxyethylene glycol acetals were synthesised through the reaction of aliphatic aldehydes such as caproic aldehyde, capryl aldehyde, capric aldehyde and lauric aldehyde with excess diethylene glycol, triethylene glycol and tetraethylene glycol, respectively. The acetal formation, in which water was azeotropically distilled by adding benzene to the reaction system, was gained a good yield of acetal type compounds. This reaction is found pseudo first order reaction at various temperatures such 70, 80, 90 and $97^{\circ}C$. Also these activation energies of reaction of acetal type products such as caproic aldehyde diethylene glycol acetal, capryl aldehyde diethylene glycol acetal, capric aldehyde diethylene glycol acetal, lauric aldehyde diethylene glycol acetal, caproic aldehyde triethylene glycol acetal and caproic aldehyde tetraethylene acetal were 17.3, 19.6, 21.2, 21.6, 15.5 and 14.7 Kcal/mole.

• Journal of the Korean Applied Science and Technology
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• v.6 no.2
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• pp.29-37
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• 1989

Using the quarternary ammonium salts as phase transfer catalyst, the nucleophilic substitution reaction of 1-chlorooctane with sodium-cyanide was investigate kinetically with respect to the formation of octanenitrile. The product was analyzed with gas chromatograph, and quantity of octanenitrile was measured. The reaction condition was considered by the effect of the reaction temperature, of the species and the amount of catalyst, of the speed of strirring, and of the concentration of reactants. The reaction was carried out in the first order on the concentration of 1-chlorooctane and sodium cyanide, respectively. The over-all order was 2nd. The activation energies for the nucleophilic substitution reaction of 1-chlorooctane and 1-bromooctane under tetrabutylammonium hydrogen-sulfate were calculated as 2.05 and 10.08kcal/mol, respectively. The effect of various caltalysts was decreased in the order of tetrabutylammonium bromide, terabutylammonium, tetrabutylammonium hydrogensulfate, and tetrabutylammonium iodide. The reaction rate was dependent on the concentration of sodium-cyanide dissolved in the aqueous phase, and the good result was shown when the mol ratio between 1-chlorooctane and sodium cyanide was one per three.

• Journal of the Korean Applied Science and Technology
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• v.32 no.3
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• pp.386-393
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• 2015

The rheological properties of complex materials such as colloid dispersion show complicated non-Newtonian flow phenomena when they are subjected to shear flow. These flow properties are controlled by the characteristics of flow units and the interactions among the flow segments. The rheological parameters of relaxation time $({\beta}_2)_0$, structure factor $C_2$ and shear modulus $X_2/{\alpha}_2$ for various thixotropic flow curves was obtained by applying thixotropic equation to flow curves. The variations of rheological parameters are directly related to non-Newtonian flows, viscosities and activation energies of flow segments.

• Journal of the Korean Applied Science and Technology
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• v.36 no.4
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• pp.1050-1059
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• 2019

The self diffusion, hole volume, and flow thermodynamic parameters of polyamide fibers were calculated from rheological parameters and crystallite size in order to study of flow segments in amorphous region. The stress relaxation of polyamide filament fibers were carried out in air and various solvents at various temperatures using the tensile tester with the solvent chamber. The rheological parameters were obtained by applying the experimental stress relaxation curves to the theoretical equation of the Ree-Eyring and Maxwell non-Newtonian model. It was observed that the rheological parameters of these polyamide filament fibers are directly related to the relaxation spectra, self diffusion, viscosities, and activation energies of flow segments.

• Elastomers and Composites
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• v.28 no.2
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• pp.103-107
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• 1993

To make new filler for conducting rubber, the sample of perovskite-related ferrite system $Dy_{2-x}Sr_{1+x}Fe_2O_{7-y}$ (x=0.0, 0.5, 1.0, 1.5, and 2.0) were synthesized at 1473K in air. $M{\ddot{o}}ssbauer$ spetrum of x=0.0 sample shows typical six line pattern with $M{\ddot{o}}ssbauer$ parameters, $I.S=3.6{\times}10^{-1}mm/sec,\;E_Q=-7.0{\times}10^{-2}mm/sec,\;H_{int}=5.19{\times}10^2\;Koe$. In case of x=2.0, the spectrum is composed of single line exhibiting coexistance of $Fe^{3+}(I.S.=3.7{\times}10^{-1}mm/sec)$ ions and $Fe^{4+}(I.S.=-1.9{\times}10^{-1}mm/sec)$ ions. With increase in x value electrical conductivity at constant temperature sharply increased and the activation energies decreased from $3.8{\times}10^{-1}\;to\;1.9{\times}10^{-1}\;eV$.

• Journal of radiological science and technology
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• v.21 no.2
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• pp.53-56
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• 1998

Highly sensitive $CaSO_4:Tm$ TLD is fabricated and their trap parameters are determined. The glow curve of $CaSO_4:Tm$ consists of three glow peaks and these peaks are isolated by the thermal bleaching method. The isolated glow peaks are fitted by a least squares method. The activation energies are 0.68, 0.82 and 1.03 eV. The frequency factors are $8.09{\times}10^8,\;9.14{\times}10^8$ and $1.03{\times}10^9/s$, and the kinetic orders are 1.37, 1.54 and 1.68, respectively. The optimum temperature range of the main peak for radiation dosimetry is between 220 and $290^{\circ}C$.

• Membrane Journal
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• v.9 no.3
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• pp.141-150
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• 1999

A novel permeation apparatus was developed which could make the on-line measurements of both flux transient and permeate composition in gas permeation. The measurement by using the per¬meation apparatus was based on the continuous-flow technique. The transient measurement allowed the simultaneous determinations of permeation characteristics, such as, permeability, diffusion and solubility coefficients, and activation energies only with one experiment. The apparatus performance was illustrated by conducting the permeation of pure gases through two glassy polyimides and a rubbery poly (dimethyl¬siloxane) membranes, respectively. A comparison of the permeation characteristics determined from the flux transients was made with the literature values for verifying the confidence and accuracy of the measurement. Also, the analysis of the permeation transients obtained was carried out for the close investigation of the permeation behaviors of gases through membrane.